1. Field of the Invention
This invention relates to electrical fittings used in the installation of electrical conduit, and namely an improved locking hub nut.
2. Background of the Invention
The current state of knowledge is as follows. Electrical conduit is a system used for protection and routing of electrical wiring. Electrical conduit is generally made of metal or plastic polymers, and protects the wiring from mechanical damage and chemical interference, e.g. water. Conduit also requires the use of special fittings for connections, end points, and so forth. Two common electrical connectors are snap-in connectors and multi-part connectors. Snap-in connectors use a snap-in ring to quickly connect to a junction box, and multipart connectors use threaded, multipart lock-nut components. Various types of wiring can be pulled into a conduit, which simplifies building design and construction as well as building renovations, since wiring can be added or replaced by pulling through the existing conduit.
However, wiring is frequently damaged during such pulls due to the interaction of the wiring on the fittings that are used, often resulting in the wiring insulation being damaged and/or removed from sections. Since the use and installation details for conduit are governed by various building codes, this kind of damage can make the difference between a successful inspection or an inspection that requires re-installation.
One way to reduce the incidence of damaging the wiring is to install the wiring in two person teams with one person feeding the wire while the other pulls it through the conduit. However, this doubles the labor cost both in terms of actual expenses as well as efficiency.
Another solution has been to use a plastic bushing to cover the sharp edges that might damage the wiring. Plastic bushings are intended to protect already installed wire during hot/cold expansion or mechanical movement. However, and although the plastic bushings are helpful for already installed wire, they are nonetheless sharp enough to damage wire during pulling and are not designed for this.
Significant problems also arise with the fittings. For instance, snap-in electrical connectors are known to be problematic for having a loose electrical connection, which can be dangerous, and they allow contaminants to enter the connection. Multipart connectors are known to be problematic for many reasons, including the inherent clumsiness of the required disassembly and reassembly, use for special tools for tightening, the potential of lost locknuts, cross-threading of the locknuts, the large amount of space used within the junction box, and the non-optional destruction of the connector that occurs during disassembly.
There remains a need for a locking hub nut that does not damage the wiring during pulling, frees up manpower by allowing one person rather than two to be able to do the pulling, has a simplified design, and which has universal threading for conduit of all currently approved sizes and materials.